Buckminsterfullerene (C60) has been shown to have a number of useful photophysical properties that have led to proposed uses including, for example, photoconductive, photochemical and photovoltaic devices, as well as photodynamic therapy. Upon irradiation, the ground state of C60 becomes an excited singlet state (1C60), which subsequently converts to an excited triplet state (3C60) in unit quantum yield through intersystem crossing. In the presence of dissolved oxygen, energy transfer from the C60 triplet state to the dissolved oxygen results in efficient production of singlet oxygen (1O2). In addition the C60 triplet state can be reduced to a C60 radical anion (C60.−) in the presence of electron donors such as, for example, amines and alcohols. The C60 radical anion, in turn, can reduce dissolved oxygen to form a superoxide radical anion (O2.−). FIGS. 1A and 1B present schematics showing various processes through which C60 can produce reactive oxygen species (singlet oxygen and superoxide radical anion) under irradiation conditions.
Efforts to harness the photophysical properties of C60 for environmental and biomedical applications have been hampered by its low aqueous solubility. Although aqueous solubility can be addressed by functionalization, the photophysical activity of functionalized C60 is substantially reduced or eliminated in many instances due to aggregation in solution. Aggregation in solution generally results in contact between the fullerene cages of adjacent C60 moieties, resulting in photoquenching of the triplet state.
Various functionalized C60 derivatives have been proposed for biomedical therapeutic applications including, for example, tumor growth inhibition, DNA cleavage, and antimicrobial activity against HIV-1. For environmental applications, it has been shown that under UV irradiation, fullerols (e.g., multiple-hydroxylated C60) can be used to form reactive oxygen species, which can subsequently inactivate MS-2 bacteriophage and other pathogens, as well as destroy chemical pollutants. However, it has not been heretofore demonstrated that microbial, viral or other pathogen inactivation can occur in the presence of visible light, which would enable the use of the sun as a natural light source to affect photochemical purification and environmental remediation. Furthermore, catalytic reuse of fullerene derivatives bound to a substrate surface has not yet been demonstrated in environmental applications.
In view of the foregoing, C60 derivatives and substrate-bound variants thereof would demonstrate substantial utility for photochemical removal of contaminants from various sources, provided that successful generation of reactive oxygen species can be achieved in such functionalized C60 derivatives. Compositions containing such C60 derivatives would have particular utility in water and air purification to remove a number of biological and chemical contaminants, while using only atmospheric oxygen and light in the purification process.